Electric heater



G. FREDRICKSON ELECTRIC HEATER Filed July 11, 1931 June 4, 1935.

2 Sheets-Sheet l GUSTA V June 4, 1935.

G. FREDRICKSON ELECTRIC HEATER Filed July 11, 1931 2 Sheets-Sheet 2 IIIIFf/III INVENTOIQJ GUSTAV F/egoz/c/(sm BY %/Mm HIS ATTORNEY Patented June 4, 1935 UNITED STATES PATENT OFFICE 2,003,855 Emo'rmc HEATER ware 1 Application July 11, 1931, Serial No. 550,137 16 Claims. (Cl. 219-13) T s invention relates to electric heaters and comprises all of the features of novelty herein disclosed. An object of the invention is to provide an improved heater using alternating magnetism as a source of heat to give rapid controllafto a large scale.

ble heat of uniform penetration in the work to be heated. Another object is to provide a magnetic gap induction heater of high efficiency. Another object is to provide an all-metal heater having a self-forming lining and improved cooling features. Still another object is to provide a heater having low voltage inductors of single turn loops and a generally compact and simplified, low-cost construction. Yet another object is to provide an induction heater capable of feeding work directly to a forging machine or the like.

To these ends and to improve generally upon devices of this character, the invention consists in the various matters hereinafter described and claimed. In its broader aspects, the invention is not necessarily limited to the specific construction selected for illustrative purposes in the accompanying drawingsin which i Fig. 1 is a perspective view of the heater wit some parts broken away and others in section.

Fig. 2 is a diagram.

Fig. 3 is a sectional view of a portion of Fig. 1

Fig. 4 is a side elevation.

Fig. 5 is a front view.

Fig. 6 is a perspective view of the inductor.

Fig. 7 is a sectional view on line 1-1 of Fig. 6.

The numerals I0 and I2 indicate two sets of laminations of ferrous material separated by spacing plates l4 and all clamped together between end plates l5 by nuts on the threaded ends of tie-bars 18. Each set of lamlnations is conveniently formed in upper and lower E-shaped sections, alternate pairs of plates meeting at the lines 20 as indicated in Fig. 5 and the intervening pairs meeting at the lines 22 to breakjoints. The

laminations enclose a generally rectangular space but have central core projections 24 extending towards one another and preferably adjacent extensionstll presenting opposed arcu=- an end of the side wall 26 by an integral cross piece 32. The side walls are hollow to form passages 34 for cooling fluid and the cross pieces 32 are likewise hollow to form connecting passages 36. See Fig. 7.

The side wall 26 is .united as by brazing, to an upright hollow leg 38 and the adjacent ends of the side walls 28 are similarly united'to upright hollow legs 40 and 4|. The upper ends of the legs 38 and 40 are united to a hollow loop member 42 and the lower ends of the legs 38 and 4| are united to a hollow loop member 44. Cooling fluid, such as water, is admitted (Fig. 6) to the loop member 42 through a supply pipe 45, the fluid first traversing the loop, then descending the hollow leg 40 to the passage 34 inone of the hollow side walls 28, crossing through the passage 36 to the hollowside wall 26, and finally going out through the pipe 48. Similarly, a pipe 50 supplies cooling fluid to the lower loop 44 and a pipe 52 carries the fluid away. The hollow nature of the foregoing parts is shown in Figs. 5

and 7 while Fig. 6 indicates the course of fiow by arrows. The side walls, loops and connecting legs are preferably composed of copper.

The loop members 42 and 44 form the secondaries of transformers 54 and 56 the magnetic fields of the transformers being carried by ferrous metal eitherln the form of wire or of laminations similar to the laminations ID. A layer of insulation 51 (Fig. 3) lines the interior of each field and encloses the loop member 42 or 44 and its primary coil, the primary coil 60 or 62 being further insulated by a layer of insulation 58. The coil 60 or 62 is preferably composedof a continuous winding of copper tubing surrounded by an insulating tube 63. The hollow tubing not only carries an electric current but also carries a current of cooling fluid, such as water, admitted through a supply pipe 54 to a branch coupling 66. A branch pipe 68 conducts the cooling fluid to the lower part of the coil 60 while a pipe l0 carries the fluid away. The couplings for the pipes are conveniently supported by a shelf 12. A branch pipe 14 conducts the cooling fluid to the middle portion of the coil 62. A pipe 16 conducts the fluid away from the upper portion of coil 62 while a pipe 18 conducts the fluid away from the lower portion. Electric current from a three-phase, three-wire generator is conducted by the pipes to the tubing of the primary coils and the fields link the primaries with the secondaries to produce therein an alternating low voltage current. One lead wire is connected to the coupling of the pipe 10 below the shelf 12,

zontal channel irons es and 95 connect the stand- I ards, and angle irons as support the shelf 12.

The shape of the air gap between the core projections 26, 24 may be varied to suit the work W which, in the illustrated construction, is a bar of steel of circular cross section fed endwise into the guide. An alternating etic held of intense magnetic flux density is set up being a part of the core. Due to hysteresis and eddy currents, the bar heats until a temperature is reached where its ermeability to magnetism is reduced. As a res t of decreasing permeability, the magnetic flux density decreases, thus causing decreased energy input to the work as its temperature rises. In other words, the work absorbs greatest energy while cold and the supply of energy diminishes progressively as it is heated. The ultimate temperature is reached when the energy input decreases to the value of radiated heat plus the heat conducted from the work to the surrounding walls. This automatic control of the ultimate temperature by the decreasing flux density is an important feature.

Heating of the work occurs internally, rather than from the outside asin ordinary furnaces, and is very rapid. When cold, the steel bar acts both as a econdary to a transformer (having the field 10 r 12) and as part of a core but, when it is heated, it acts only as a secondary. The bar is also self feeding endwise in the guide because, as the foremost end heats and loses its magnetism, the following portions of the bar which are still magnetic are drawn forward like the core of a solenoid until they too lose their magnetismr The inductor 2t, 28 is preferably made of copper or other conductor that will oxidize and so'form a lining of poor electrical conductivity at the gap, thereby preventing buming of the bar by direct contact at 30. The

is' initially part pf a core and then acts as a secondary -to a. transformer, the heater is to be distinguished from a so-called coreless furnace and from a core type induction furnace and may be termed a. magnetic gap induction heater. The shape of the gap will'vary with the shape of the work but is such as to give minimum distance betweenthe core projections 24, .24 with maximum area therebetween. Thus the flatter the bar, the closer the projections 24, 24 will be made 'to approach one another. The current vaiue required for inducing intense magnctismis thus reduced to a um with. a resulting high power factor and efliclency, and the efliciency becomes mo e pronounced when the metal is a thin sheet with the gap shaped to conform to it.

All non-magnetic materials act as a secondary to-a transformer when placed in the air gap and are heated to a-temperature dependent on the current supplied to the" transformers and .on the 32, 28, about the work. Inasmuch as the work' aooasss electrical resistance. The magnetic field reins constant under constant current conditions.

It will be noted that the apparatus herein shown comprises two heaters combined in one 5 and energized from the primary coils es and $2. The Scott or T-connector produces two single phases controlling one heater and this balances the load on a three-phase, three-wire generator. The heated bar may be led from the heater di- 10 rectly to a'forging or heading machine which shapes and cuts oil the foremost end as fast as the bar advances. The low voltage at the inductor is an important eguard in operating the P machine. 15

I claim: 7

1. In an induction heater, a pair of straight side walls spaced apart to embrace and guide a piece of work therebetween and forming a portion of an induction loop, a core surrounding the side walls and the work-piece, ,and means for supplying altemating. current to the induction 7 loop to heat the piece and cause it to advance between the side walls; substantially as described.

2. In an induction heater, a pair of hollow side 25 walls spaced apart to embrace and guide a piece of work therebetween and forming a portion of an induction loop, means for supplying cooling medium to the hollow side walls, a core surrounding the side walls and the work-piece, and means for supplying alternatmg current to the induction loop; substantially as described.

3. In an induction heater, a pair of hollo members spaced apart to embrace a piece of work and forming a portion of an induction loop, means for supplying cooling medium to the hollow members, a core surrounding the hollow members and having extensions carried close to the work-piece, and means for inducing alternating low voltage current in the hollow members; substantially as described.

4.111 an induction heater, a pair of side walls spaced apart to embrace and guide a piece of work and fg a portion of an induction loop, a core surrounding the side ,walls and having core 45 projections substantially conforming to the work-piece, and means for supplying alternating current to the inductionloop; substantially as described. I

5. In an induction heater, a pair of side walls spaced apart to embrace and guide a piece of work and forming a portion of an induction loop,

a core of magnetic material surrounding the side walls, meansdor supplying alternating current to,,theinduction loop, and means for cooling the side walls; substantially as described.

In an induction heater, a pair of sidewalls spaced apart to embrace a piece of work and forminga portion oi; an induction loop, a core: surrounding the side walls and having projections 0 entering between the side walls and providing a gap for the work-piece, and means for supplying an alternating current to the induction loop; substantially as described.

- 7. In an induction heater, 8. pair of side walls forming alportionigf an induction loop, the side. walls having extensions leaving a space substantially conforming to a piece of bar stock to guide the latter, a core surrounding the side walls and the bar, and means for supp alternating current to the induction loop to heat the piece and cause it to advance endwise between the side walls substantially as described. W

8. In an induction heater, an inductor having a gap for a piece of work and composed of material which when heated produces a non-conducting oxide at the surface, the surfaces of the inductor at the gap conforming to the sides of the work to guide the latter endwise through the gap, a core forming a magnetic linkage around the inductor and through the work-piece, and means for supplying'alternating current to the inductor; substantially as described.

9. In an induction heater, an inductor having straight side walls arranged to closely embrace and guide a straight piece of work, a core forming a magnetic linkage around the inductor and through the work-piece, means for supplying alternating current to the inductor, and the side walls next to the work having a self-oxidizing non-conducting lining; substantially as described.

10. In an induction heater, a core having a gap substantially conforming to a straight piece of work, an inductor having a gap substantially conforming to the work-piece, the gap forming surfaces of the core and of the inductor substantially enclosing the work-piece on all sides, and means for supplying alternating current to the inductor; substantially as described.

11. In a magnetic gap induction heater, an inductor having a pair of side walls to embrace and substantially conform to an elongated bar of magnetic material, a core having a gap substantially conforming to the bar, means for creating an alternating magnetic field at one portion of the bar to heat said portion of the bar to a. temperature which decreases itspermeability whereby the bar is caused to advance between the side walls; substantially as described.

12. In an induction heater, a core having a gap for a piece of work, an inductor having straight side walls extending through the core and embracing and guiding the work, and the ends of the side walls being electrically con-. nected; substantially as described.

13. In an induction heater, a core having a gap for a piece of work. an inductor having straight side walls extending through the core and guiding the work, aloop outside of the core. and having electrical connections with the side walls, and means for supplying alternating current to the loop; substantially as described.

14. Inan induction heater, a core having a gap for a piece of work, an inductor having straight side walls extending through the core and guiding the work, legs connected to the side walls, and a loop connecting the legs; substantially as described.

15. In an induction heater, a core having a gap for a piece of work, an inductor having side walls extending through the core, a cross piece connecting the side walls at one end, and a loop having electrical connections with the side walls; substantially as described.

16. In an induction heater, a core, an inductor having side walls within the core and spaced apart to form a gap to receive a piece of work,

a loop having electrical connections with the side walls, the'loop and side walls being hollow to circulate cooling fluid, and means for supplying alternating current to the loop; substantially as described.

GUSTAV FREDRICKSON. 

